The invention relates to electric lamps and particularly to plastic electric lamp reflectors. More particularly the invention is concerned with plastic body lamp reflector with a protective barrier layer.
Headlamps used to be made from glass. The glass rarely reacted chemically with the lamp fill materials, and rarely if ever contributed, or outgassed materials into the lamp process. Automotive headlamps are now predominantly plastic, and the trend is to apply plastic to all vehicle lamps. To lower material costs, the shell material is extended or filled with less expensive materials, such mica or glass fiber. These filled resin materials are referred to as bulk molding compounds, or BMC. The fill material tends to cause a rough surface. The shell is then frequently coated with a liquid base coat to prepare the reflective regions to have a very high degree of smoothness. These smoothing materials, such as an acrylic urethane, flow over and fill in the crevices left in surface of the shell. The base coating material is expensive. The base coating can also be difficult to properly apply, as it tends to run, drip and splatter. Also, pits in the reflector shell can be filled by the liquid, but only dried to have surface skin. The interior liquid then erupts during evacuation, leaving a surface hole, and splattered material in the equipment. The base coating can also be an environmentally offensive material. The flow coating method is further described in U.S. Pat. No. 5,493,483. There is then a general need for reflector without a base coat. The hard, smooth base coat layer is then metallized, for example by vapor deposition or sputtering of aluminum on the shell interior to form a mirror like reflector. Although not strictly necessary, the reflective coating is then coated with an environmental sealer to limit or stop water or other materials from tarnishing the mirror surface. The sealer is commonly silicon monoxide.
So called, no base coat reflectors have been developed. Relying on a combination controlled material formulation, tooling and processing, reflectors can be made with a sufficiently smooth surface that no base coat is needed, even if the resin material includes fillers. The metallization layer is then applied directly on the formed resin surface. Elimination of the base coating is considered to be a significant improvement in reflector manufacture. Unfortunately, the resin materials can outgas solvents, or other low molecular weight resin constituents that then drift freely in the interior cavity. It is a normal characteristic of the raw plastic material to include mobile solvents or similar mobile components that enable the material to be soft and pliable for molding. After molding, the remaining solvent or similar material is superfluous and is normally baked out or allowed to outgas over time. These outgassed materials can condense on the interior surfaces of the vehicle lens, reflector or lamp. The condensed material fogs the light source, the reflector and the lens, and thereby reduces the effective light output. The outgasing material can also lessen the adhesion of the metallization layer, resulting in pin holes, delaminations, wrinkles and similar reflector defects, resulting in uncontrolled light, or glare emitted from the lamp. There is then a need for a no base coat vehicle headlamp reflector that resists outgasing from the shell material.
Headlamp reflectors made from filled bulk molding compound (BMC) have been pre-baked at high temperatures to drive off outgasing materials. This takes time and energy. Alternatively, the reflectors have been flow coated with a base coating which had the effect of encapsulating the surface. Both these methods reduced the out-gassing of the headlamp reflectors at moderate operating temperatures of around 350xc2x0 F. The new smaller fog lamps and headlamps use higher wattage bulbs and generate more energy thus raising the maximum operating temperatures found in the headlamp reflector systems to above 425xc2x0 F., resulting in additional outgasing. The higher operating temperature forces a reconsideration of the material choices for headlamp reflectors. While base coating may continue to work as a sealer, base coating is still an expensive and environmentally challenging process. The no base coat headlamp design reduces the cost of forming a durable headlamp reflector by eliminating the base coat material, the coating equipment, the VOC emission controls, shortens the construction cycle time and reduces the labor required to run the process. Unfortunately, eliminating the base coat, eliminates the encapsulation that protected the lamps from the outgas materials. There is then a need for a practical means for sealing shells from outgasing.
A common protective surface coating for the aluminization layer is a plasma deposition of silicon monoxide on the surface, such as Balzer""s Protectyl BD 481 065 T or Dow Coming""s 200 fluid 0.65 CST. The silicon monoxide protects the aluminization from water attack, but does not protect against water from condensing on the surface or protect from outgassed resin material from collecting on the reflector as a haze. The silicon monoxide is relatively inexpensive to apply in terms of material, and in labor and equipment. There is then a need for an improved surface layer material to eliminate out gassing from the support layers and to protect metallized reflector surfaces from the resulting condensations.
An improved plastic reflector for use with an electric lamp maybe formed from a molded plastic reflector made from a bulk molded compound. The reflector has a first layer of a plasma polymerized material adhered to the inner surface forming a thin film that smoothes the surface of the bulk molded compound; a metal layer of deposited metal adhered to the first layer, and protective overcoating layer adhered to the deposited metal layer.